This invention relates to photography, and more particularly to a method for controlling photographic lenses.
An internal-focus lens group is often used in a camera to reduce the size and weight of the overall lens. Referring to FIG. 1, a standard internal-focus lens 100 is shown. The mechanism or mechanisms for moving the lenses, as well as any control electronics, are not shown for clarity. The internal-focus lens 100 includes a number of other lenses, including a focus lens 102, which itself can include one or more elements. The focus lens 102 can move between a rear focusing position 120 to focus on an object at infinity and a front focusing position 122 to perform macro focusing. Macro focusing is typically utilized when a photographer wishes to focus on an object located particularly close to the camera itself. In one embodiment, the focus lens 102 focuses an image on an image detector 130 such as a charge-coupled device (CCD), or photographic film. In another embodiment, the image detector 130 is not used, and the focus lens 102 creates an image that can be viewed with the human eye. In such an embodiment, the lens 100 may be used in a binocular or telescope device, or other type of viewing device. The internal-focus lens 100 can include a single zoom lens adapted to move relative to the focus lens 102, or a zoom lens group 104 having a first zoom lens 106 and a second zoom lens 108 adapted to move relative to one another and the focus lens 102. Each zoom lens 106, 108 can include one or more elements. By moving the zoom lenses 106, 108 relative to one another along the optical axis 110, the degree of magnification can be controlled. When the zoom lenses 106, 108 are close together, they are in a telephoto position where a greater degree of magnification is provided. When the zoom lenses 106, 108 are further apart, they are in a wide-angle position where a lesser degree of magnification is provided. The second zoom lens 108 moves forward to a front zoom position 124 when the zoom lenses 106, 108 are closest together for the greatest magnification, and moves backward to a rear zoom position 126 when the zoom lenses 106, 108 are furthest apart for the greatest wide angle view.
In order to save space within a camera, the front focusing position 122 of the focus lens 102 may be located in front of the rear zoom position 126 of the second zoom lens 108. Thus, the focus lens 102 can collide with the second zoom lens 108 within a potential collision zone 128 between the front focusing position 122 and the rear zoom position 126. Such a collision can damage the focus lens 102 and/or the second zoom lens 108. During normal operation of the camera, the focus lens 102 and the second zoom lens 108 typically will not collide, as the macro feature is rarely used in normal operation, and it is usually used when the zoom lens group 104 is in telephoto position. However, even a single collision between the focus lens 102 and the second zoom lens 108 can ruin those lenses, requiring the user to repair them at some expense, or discard the camera altogether.
A focus lens and a zoom lens group are controlled in an internal focus camera to maintain a minimum safe distance between the focus lens and an adjacent zoom lens.
In one aspect of the invention, the focus lens and a zoom lens group having a first zoom lens and a second zoom lens are controlled separately from one another.
In another aspect of the invention, the positions of the focus lens and the second zoom lens in the zoom lens group are tracked.
In another aspect of the invention, the focus lens and the second zoom lens are controlled to approach no closer to one another than a minimum safe distance. In this way, collision between the focus lens and the second zoom lens is prevented, thereby preventing damage to the lenses.
The invention will be more fully understood upon consideration of the detailed description below, taken together with the accompanying drawings.